Field of the Invention
The present invention relates to the processing, preparation, and preserving of food.
Description of the Art
In 2002, the average American consumed 284.4 pounds of fruit, 65% of which was processed. In fact, forty four percent of the vegetables produced in the United States are processed in some way. For most fruits and vegetables, “processing” includes blanching which is a procedure used to inactivate the enzymes responsible for quality deterioration of fruits and vegetables. This inactivation is normally achieved by exposing fruits and vegetables to an elevated temperature (70-100° C.) for a period of time (generally 1-10 minutes). Typical energy sources include hot water, steam or microwave.
Besides the inactivation of enzymes, blanching also operates to reduce microbial contamination, to stabilize color, and to facilitate further processing and handling.
Blanching has generally been done utilizing hot water or steam. This requires a large amount of energy, however, and can cause significant losses of nutrients, phytochemicals, and/or flavors. Moreover, hot water or steam blanching can also result in aesthetic deterioration of fruits and vegetables, making them less appealing to consumers.
Since blanching with hot water or steam at high temperature may cause undesirable changes in product texture, low temperature blanching at 50-70° C. has been attempted with various fruits and vegetables, including carrots, bell peppers, and sweet potatoes (Dominguez et al., 1996; Fuchigami et al., 1995; Stanley et al., 1995). In general, low temperature blanching was found to improve the texture quality of the products, but suffered from the shortcoming of longer processing times.
High pressure blanching has also been studied as a possible alternative to steam blanching. For example, pressures of between 400 to 900 MPa, applied for 5-10 min, have been shown to inactivate up to 88% of peroxidase in green peas. (Guaglia et al., 1996; Master et al., 2000). However, high pressure blanching significantly reduces the firmness of the treated samples, and the process itself requires expensive equipment which is also expensive to operate.
Although hot water and steam blanching is a common processing step for vegetables, alternatives have been sought especially for delicate fruit which are easily damaged. Various methods have been attempted such as chemical inactivation of enzymes, avoidance of contact with oxygen, and use of various antioxidants. Examples of alternative practices include dipping the fruit in diluted ascorbic or citric acid solution, or exposing them to sulfur gas before freezing, canning, or drying in order to prevent enzymatic browning (FMC, 2003; Dauthy, 1995). The shortcomings of these alternatives, however, include extended processing time, increased expense, and undesired flavors.
Some researchers have tried to use microwave energy to blanch fruits and vegetables. Microwave blanching, however, is a very expensive technology due to high capital cost and low energy efficiency. Additionally, microwave energy can also cause significant losses of nutrients and phytochemicals, as well as quality deterioration due to uneven heating inside the food products.
In short, blanching technologies to date all suffer from one or more shortcomings.
In addition to blanching, food processing also frequently includes dehydration or drying. In fact, dehydration is often performed after blanching and is itself the most energy consuming step in food and agricultural product processing.
Dehydration is typically achieved through the use of hot air, usually generated by gas-fired heaters and electrically driven blowers, directed through an air tunnel. This process suffers from relatively long drying times, high energy consumption, and unpredictable microbial counts in the finished products. Moreover, long drying times can cause significant losses of volatile compounds, reducing the desirable flavor characteristics of the finished products. Furthermore, most dryers and dehydrators are normally specialized for only one commodity, which increases operating costs and capital outlay. Finally, high drying temperature and high airflow rate also combine to cause deterioration in the quality of finished products. In the case of rice processing, for example, high temperature drying significantly reduces the amount of marketable product, which has a direct and adverse impact on the economic value of the paddy rice to both rice farmers and rice processors (Pan, 2003).
Other dehydration methods have also been tried. Solar drying, for example, is simple and economical, but the products are subject to insect and rodent attack, wind damage, sudden rain, soil entry and other problems. Drying can also be done with osmotic dehydration, immersion chilling, and freezing in concentrated aqueous solutions (Torreggiani et al., 2000). These methods all have significant adverse impact on the quality of the finished product or high production costs.
Food processing also frequently requires a freezing step. One approach that has been attempted is to combine blanching, dehydrating, and freezing. Such products are often referred to as “dehydrofrozen products.”
The dehydrofreezing process offers several advantages over conventional freezing, including (1) energy savings due to lower water load to the freezer; (2) reduced costs related to transport, storage and wrapping; (3) better quality and stability (color and flavor); and (4) superior thawing properties (low drip loss). The moisture content of typical dehydrofrozen products is reduced 40-60% of the original content. These products also need to be processed quickly in order to mitigate the quality change caused by the blanching heat. Conventional convective drying, which is how these products are normally processed, is problematic because it requires a relatively long period which often results in product deterioration.
For the foregoing reasons, the food and agricultural processing industries have been seeking efficient and cost effective alternative blanching and drying technologies for producing high quality, more versatile products. One alternative that has shown great promise is the use of infrared technology.
The use of infrared technology in food processing, including the separate processes of blanching and dehydration, has been studied but has not been widely implemented because of problems involving lack of effective protocols as well as general reliability. Infrared heating is promising, however, because it can potentially shorten processing times, improve energy efficiency, reduce the space needed for equipment, and generally enhance production and quality.
What is needed is a method and apparatus that can employ effective infrared processing technology that can be used to blanch and dehydrate food in general, and dry fruits and vegetables in particular. The ideal system will provide the ability to perform blanching and dehydrating/drying separately or simultaneously. The inventors have been able to achieve just such a method and apparatus.